


Thinly Sliced

by snasational



Series: Classic Vs The Multiverse [4]
Category: Undertale (Video Game)
Genre: Alternate Universe - Canon Divergence, Cross Sans - Freeform, Cross is kind of horny in this one sorry, Implied/Referenced Self-Harm, Knifeplay, M/M, Underverse
Language: English
Status: Completed
Published: 2020-12-26
Updated: 2020-12-26
Packaged: 2021-03-11 00:21:25
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,119
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28336068
Author URL: https://archiveofourown.org/users/snasational/pseuds/snasational
Summary: In which Sans finds Cross instead of Ink.
Relationships: Sans/Sans (Undertale)
Series: Classic Vs The Multiverse [4]
Series URL: https://archiveofourown.org/series/2065212
Comments: 8
Kudos: 112





	Thinly Sliced

**Author's Note:**

> SOME THINGS TO NOTE:
> 
> -I have never, ever written Cross before. This is my first attempt! My apologies for anything OOC  
> -My Classic is different from Underverse's Classic. So is my Frisk  
> -This is set some time before Underverse.  
> -This might be multichaptered in the future  
> -This fic briefly mentions self harm  
> -Not Beta'd or proofread. Please forgive any mistakes you find. It is 3am and I am very tired.

He didn’t know you could take a wrong turn in a shortcut. 

Granted, Sans was beyond distracted. Thinking about Frisk and how he was going to fix their predicament tended to do that to him. He loved the kid to death, and most importantly he wanted everyone to be happy and on the surface and not murdered by the soulless ghost of a suicidal ten year old. Yeah, that’s a mouthful for him too. 

So when they stumbled upon his porch earlier than normal with a face full of tears, he crumbled. Last genocide was a particularly bad one, and while Sans wanted nothing more than to punt them across Snowdin he wasn’t cruel. 

“Do you hate me?” He remembers them asking with a shaky voice. They were wrapped up in the coziest blankets Sans could fine. 

“No. Never.” And it was the truth. “Just...disappointed.”

That had hung their head down low. “I don’t know how to make it stop, Sans. Chara, the resets. I don’t know what to do.” 

Maybe, if the kid was an adult capable of understanding the gravity of these kinds of things, Sans would’ve stayed pissed. But Frisk didn’t deserve it. And in a way, neither does Chara. They can’t help the fact that they’re soulless. Taking away a soul takes away the personality and fundamental morals.

The real Chara was probably a whole lot different than the thing sharing a body with his kid. He feels sorry for them, he really does. Sorry doesn’t fix anything though. 

“It’s alright kiddo.” He sat next to them on the couch and ran a gloveless hand through their hair. It had been quite a few resets since he’d done something like that. “We’ll figure it out.”

“Pinky promise?” 

He held out a boney pinky. “Pinky promise.”

The smile was worth it. Frisk has always been so much more emotional than people give them credit for. And fuck, Sans loved them like they were his own. In a way, they truly were. Nobody understood him like Frisk did. Stuck in a timeless loop with no escape in sight. 

(And. Maybe, just maybe being around them reminds him of a time when Papyrus was itty bitty. Is it selfish to yearn for those times, he wonders.)

So, you have to forgive him if his mind is on other things. Shortcutting normally came to him as easy as blinking. He hasn’t gotten a shortcut wrong since he was a teenager. His thoughts are such a cacophony of...weirdness that he supposes his magic reflects that.  _ Snowdin,  _ he thinks. 

Nothingness is what he gets. 

He steps into a field of white. White that never seems to end. And in front of him is a crumpled up figure of even more white and black. Surrounding this person is a deep shade of purple. The liquid seems to be everywhere. Coating the texturless ground and staining the poor guy’s face. 

A face too much like his own for comfort. 

Sans ought to be a lot more surprised by this. But, all things considering, he’s really not. Tons of weird shit happens to him, this is just the icing on top of the cake. The sad skeleton looks at him with eyes of red and black, those lights shining with pity and fear. Much like his kid had earlier this morning. 

Man, today just isn’t Sans’ day. 

“Hey buddy.” He greets casually. Sans stuffs his hands in his pocket and strolls over to him. The figure flinches and scoots back. But Sans has dealt with his fair share of child wrangling. Sitting next to a scared adult is easy peasy compared to that. He plops down a couple of feet to his left. 

“This place is kind of depressing isn’t it?” 

The other skeleton looks to Sans briefly before he trains his eyes on purple puddles. He curls himself up into a ball, hugging his knees to his chest. “...To say the least.” If the appearance hadn’t given it away, the voice sure did. 

“Heh. Well, I don’t suppose you have a name?” 

At first, he thinks he won’t answer him. But softly, he tells Sans. “Cross.” 

Sans expects them to share a name. His surprise doesn’t reflect on his face. “Cross, huh? That’s...interesting.”

Cross tenses. “What? You don’t like it?” His tone is defensive, and he peers at Sans from over his arm with a look of offense. Geez, that’s another difference they have. Sans sure as hell doesn’t get offended so easily. 

“Did I say that?” He challenges. “No need to be so  _ cross  _ with me.”

Silence. And then a snort. “A pun? Really?” 

“Yeah.” Sans grins. “What? You don’t like it?” He parrots teasingly.

Cross frowns at him, but gradually he unwinds his body until he’s sitting cross legged. His hands rest in the gap between his legs. It’s kind of childish, if Sans has to be honest. “I like them. I...I just wasn’t expecting it, that’s all.”

“Course you like them.” He hasn’t met a single Sans that doesn’t like them. Granted, Cross is the only other Sans he’s ever met before. Even if he’s certainly...different. Cross sort of reminds him of those cartoons Alphys is obsessed with. His whole outfit setup just screams something out of a human’s fantasy storybook. 

Not that he’s complaining. Sans kind of digs it. He would personally never wear it. All those straps scream too much work. Although…

Sans eyes the golden heart necklace with interest. 

(His kid is standing at the end of the judgement hall. Except it’s not really his kid. That look in their eyes, so lost and desolate...it’s not Frisk. Around their neck sits a heart locket. Frisk doesn’t like jewelry. They say that it agitates their skin, and that it makes them feel heavy and constricted. 

When he sends bones through their chest, that locket breaks off its chain and comes skidding towards him. His slippers stop it’s slide. It cracks open at the force. Inside, an engraving and a photo. “Best friends forever.”

The children in the photo look so, so small. A monster and a human no older than a decade. Too small to die the way they did. The injustice of it all sickens Sans. 

His kid looks small too, coated in blood and lying dead on the floor. He kicks the heart away and stumbles towards Frisk’s body. He drops to his knees and pulls the limp form into his lap. Frisk loves it when he does this. Babying and pampering them. They told him once that their parents never did that for them.

“I’m so sorry.” He tells the dead body. He strokes their hair and presses his teeth against their wet temple. “You understand why I have to do this, right? Next timeline will be better. I love you.”)

“...Why are you here?” Cross breaks the silence. Sans blinks. He was daydreaming again. He’s getting real bad about that lately. 

“I dunno. I took a bad shortcut, I guess.”

“Shortcut?” Looks like they don’t have the same abilities, either. 

“You ask a lot of questions, buddy. My turn.” 

Cross pouts but lets Sans ask away. 

“So. The elephant in the room.” He gives Cross a pointed look. The other skeleton just stares blankly at him. “...Why are we sitting in a big field of absolute nothingness?” 

Silence. And then Cross is crying again, and Sans feels like an absolute asshole. Jesus, he should’ve asked a nicer question. Now he looks like the biggest douche in the world. 

“It’s all  _ gone _ .” He chokes out. He shoves his face in the palms of his hands. “Everything. Everyone. They’re all gone and now I’m all that’s left and-”

“Okay, okay. You don’t have to keep going.” Against his better judgement, Sans scoots closer to him and pats him on the shoulder. Cross flinches but makes no move to make him leave. “I get it. Say no more.”

A genocide route, it seems. But why is there literally nothing left? It’s confusing. This whole situation is confusing. But Cross is too emotionally volatile to answer any more questions with clarity. Sans wishes he didn’t feel the need to be so technical about everything. It’s something that Gaster trained into him at a young age.

“I’m sorry.” Cross sobs. “You must think I’m weak.”

“Nah.” If Sans had the ability to cry again, he probably would. All the time. “Just means you have feelings. Congratulations to not being an emotionless dick, by the way.” 

Cross giggles hysterically, but they taper off into more strangled wails. Sans goes from patting his shoulder to rubbing his upper spine soothingly. Not his first rodeo in the comforting department, that’s for sure. Eventually, he calms down enough until all that’s left is ragged breaths.

He wipes his face with his sleeve and when he looks at Sans again his expression seems to be a lot better than it did before. Nothing like a good pity session to boost one's morales. “You okay buddy?”

“Dude.  _ No _ .”

Well, Sans applauds him for his honesty. “I felt that.” 

A comfortable silence falls between them. Sans never stops rubbing his back, and subtly Cross leans close to him. “I...will you have to leave soon?”

Most definitely. He’s got a needy brother and a depressed pre-teen sitting in his house. He’s not going to leave his family no matter how much he wants to stay and comfort the distraught skeleton. “Yeah.”

Cross’ face twists again, but this time no tears fall. Something thoughtful flashes through him. And, it’s almost like he’s battling with himself on something internally. Sans watches with fascination as his face changes a thousand expressions all at once. Is he that expressive? His face is kind of glued in a permanent grin, but Cross manages to frown and grimace and smirk. 

It’s intriguing. What else is different about them? 

Cross pulls away and Sans lets his hand drop back to his side. “Will you ever come back?”

Probably not. A shortcut like this is a once in a lifetime happening. Hopping the multiverse is vastly different than hopping locations. Sans doesn’t even know how he pulled this off in the first place and he isn't too eager to figure it out. His world has enough problems as it is. Cross must read it on Sans’ grin, because he wilts even more. 

“I’m so lonely here.” He tells Sans.

This feels oddly manipulative. Sans nods his head, empathetic. “I would be too.” 

“Please. Please come back.” Cross pleads. He gets up in Sans’ personal space, desperation written all over his posture. “I’m going insane with just me and-” He cuts himself off. “The nothingness, like you said.”

Another fucking promise. Sans can feel it coming from a mile away. He’s become an expert at that, by now. Sans can’t deal with any more of them. He promised Toriel he would protect Frisk. He promised Frisk he’d help them stop the resets. He promised Papyrus he would wake up earlier and start contributing more. All these stupid fucking promises. 

But Cross looks pitiful. 

(A crying child. 

“It hurts!” They wail pitifully. Sans made a mistake. Instead of flinging them on their neck and giving them a quick and clean death, they land on their spine. The noise it made when it hit the floor made him flinch. The agony must be unbearable. “Sans, please, it hurts. It hurts, I can’t-”

He fires a Gaster Blaster in their face. He can’t take it anymore.

A few minutes later a blank child stands at the end of the corridor. Frisk’s screams reverberate in his skull.)

“...How about this.” Cross perks up at Sans’ voice. His eyelights are so unbelievably hopeful. “How...how about you come with me.”

He could explain this to Papyrus, somehow. His brother was always the best about being understanding. Their guest bedroom is Frisk’s right now, but he’s sure his alter wouldn’t mind bunking with Sans.

“But…I can’t leave my world.” If Sans could properly frown, he would. He was not expecting a rejection to his proposal. “If there’s still a chance I can save it, then I have to stick around and do so.”

He should just take the answer and leave. One less problem on his plate. However, his mouth speaks before his head can take hold of it. “And how are you going to do this without any help?” He asks, genuinely curious. 

Cross stutters. “I…”

“You could be waiting here for an eternity, you know. Have you ever heard of the void?” 

The other shakes his head. 

“It’s a place full of nothingness. There is no time, or a concept of existence. You’d basically be doomed to the same fate here if you waited for an opportunity to come to you. Buddy, it would drive you insane.” Why is he trying so hard to change this guy’s mind? He should just drop it and go. 

There’s a spark of hesitance in him though. And Sans exploits it to the best of his abilities. 

“I can’t just abandon them.” He tries. 

“You’re not. Think of it more as...working away from home. I used to be a scientist, this kind of stuff was my specialty. There’s plenty of resources. I could try to help you, I guess. I’m kind of assuming you don’t-”

Cross cuts him off by pressing his teeth to his.  _ “Thank you.”  _ He says against Sans’ mouth, voice full of so much gratitude and appreciation. 

He’s frozen. Awkwardly, he gives Cross a friendly pat on the shoulder but does nothing to dislodge the skeleton from him. Maybe a kiss is a cultural thing? He’s really missing something here. If he had been coming onto Cross then it was entirely unintentional, but correcting the issue seemed like it would be too much work. 

When Cross pulls away, he’s beaming at Sans like he hung the moon and stars just for him. It makes Sans blush. “Okay, come on, let’s get you to my house.”

Luckily, he has no issue shortcutting back to his world.

*

“This is a pigsty.” Cross informs him when they shortcut into his bedroom.

“I know.” Sans almost sounds proud. Cross gives him a disgusted look. That morphs into horrification when he takes a look at Sans’ self sustaining trash tornado. “I see the trash-nado has caught your attention.”

“... _ Disgusting _ .” 

Well, at least he didn’t roll his sheets into a ball out of boredom this morning. He doesn’t move a lot in his sleep, so the bed is still relatively made. Sans slides out of his jacket and kicks his slippers off. 

“I know.” He repeats. His bed looks so alluring after a long day. “Make yourself at home, I have to read to Papyrus and tuck the kid in.” 

Sans walks out of the bedroom before Cross can say anything else. He goes to Papyrus first, and then after that he makes sure Frisk is layered in as many blankets as possible. Skeleton monsters don’t exactly feel temperature the same way others do, so the skeleton brothers felt no need to spend anything extra on heating utilities. 

Frisk is really making him regret that decision. They seem comfortable enough though, and that’s all that matters.

When he makes it back to his bedroom half an hour later, Cross is sitting on his mattress. To his surprise, the guy has taken it upon himself to clean his room to the best of his abilities. There’s not a single sock on the floor, and all of the trash that isn’t in the tornado has been stuffed into a trashcan Sans hasn’t used in at least a month. Even the treadmill looks cleaner than normal, somehow. 

“...Thanks?” He closes the door beyond him after staring at his room for a solid minute. 

Cross shrugs. “I’m not programmed to be lazy like you. Cleaning doesn’t bother me.” 

Another thing to mark on the differences checklist. Sans has accepted his laziness, so he’s not offended by the bluntness. He simply chuckles and strolls over to his bed before crawling into it and laying on his side. He’s beyond tired. Cross watches him get situated next to the wall but he makes no move to get under the covers himself. 

“Are you not tired?” Sans finally asks. Cross shakes his head. 

“Not really. I’m actually kind of excited right now. I can’t…” His eyes get a faraway look to them. “I can’t wait to see them again.”

Sans’ heart twangs. Yeah, he hopes he can help him achieve that dream. Eventually. One day. He never said  _ when  _ they’d figure out a solution, after all. But that’s a problem for another day. “Understandable. But you should at least try and sleep. We’ve kinda got a busy day tomorrow, after all.”

“...” He’s still looking at Sans. His expression is unreadable. It’s starting to make him feel a little uncomfortable. “Dude?”

“Hm?”

“You know, I’m really really thankful for you doing all this for me.” 

Sans makes a noncommittal sound. He closes his eyes. “No biggie.”

He’s suddenly got an armful of skeleton. Well, at least he’s actually laying down. “I’d like to show you just how much I appreciate it.”

Sans has become painfully aware of their closeness. His eyes snap open and he squirms a bit, but Cross has got his arm secured over Sans’ side. He’s sandwiched between him and the wall now. Sans tries to will the flush from his face. 

“Listen, buddy, you really don’t have to show any sort of appreciation. I don’t mind, really.”

Magic still coils in his pelvis. How long had it last been since he had sex, anyways? Well over a year, not including the resets. Not because of a lack of willing partners but because of a lack of motivation. His magic is making him realize his self neglect, and it all comes in the form of this broken little skeleton that has his face and voice. 

Is it fucked up to want this? A few minutes ago Sans would’ve firmly said no, but now that his body has shown interest Sans is having a hard time. 

“But I want to.” Cross insists. His hands sneak underneath Sans’ shirt and caress at the floating ribs. Sans sucks in a breath. 

“Cross,” He accidentally whines. “You really don’t have to do this.” 

“Please.” 

Sans has always been a sucker for some tasteful begging. He sighs. This is a tough decision to be making right now. But he’s tired and horny, so clearly his judgement is a little fogged up. 

“...Fine. Only if you’re quiet.” 

Teeth are on his again. Soft and delicate. A chaste kiss that sends a warm feeling tingling all throughout his body. “You won’t regret this.” 

Sans sure hopes not, considering the fact that he dragged Cross away from his universe. 

When Cross unhinges his jaw, a purple tongue falls out of it. Sans matches his actions, and when their tongues intertwine it’s like magic buzzes. Their tactics aren’t the same; Cross is earnest and energetic while Sans is lazy and relaxed about it. This leads to a slobbery, wet kiss that has dark purple spit sliding down both of their faces. 

Mister clean prissy Cross doesn’t seem to mind it at all. He hums into the kiss before breaking away to take off his coat.

This proves to be a challenge. Sans laughs a little bit, because honestly Cross was asking for it with those straps. So inconvenient. Eventually they get it, and Sans’ shirt follows suite when it’s tossed on the floor. That black undershirt goes too, and bare bone is exposed for Sans to admire

“Pretty.” Cross breathes out. 

Sans would disagree. Chipped bone litters his ribcage from a much more...darker time in his life. Mentally, that is. Back when he still cared enough to do stuff like chip his own bone. Maybe they’re more alike than Sans originally thought. Slashed bone litters Cross’ ulna and radius, much too neat and practiced for it to be unintentional. 

Some of them look fairly recent. That’s a habit that definitely won’t be continuing. That’s a conversation for later though.”I could say the same to you.”

Cross breathlessly giggles and kisses him again. And again. And  _ again.  _ His tongue is numb by the end of it. At some point, their pants have been shucked off and Cross straddles Sans’ hips. The glow of their ectobodies brightens the room and casts them in hues of purple and blue. When did they even turn off the lights? Sans doesn't remember nor does he care.

His dick is so hard that he’s scared it might actually break off. And, since Cross is taking his time kissing him as enthusiastically as possible, Sans figures he ought to take matters into his own hand. With surprising physical strength, he flips Cross onto his back. The other yelps at this action, clearly not expecting it. Sans’ grin widens. 

“Sorry. Getting a little impatient here, if you couldn’t tell.” 

Cross smiles sheepishly. His legs wrap around Sans’ waist and urges him forward. The tip of his dick grinds roughly against folds and the feel of it draws a moan out of Sans. Low and husky, Cross echoes with one of his own. 

“Wait, wait, before you put it in could you- could you just- Oh, here, I’ll show you.” Sans balks when Cross summons an actual knife. How did he do that? There’s no mistaking the shine of metal. After all, he’s intimately familiar with the appearance of one. He presses the handle into Sans’ hand.

“While you’re fucking me, I want you to hold this against my neck.” A gorgeous purple hue colors his cheekbones. “Only if you want too, though.” 

Sans stares at the knife. Then Cross. Then the knife again. Wow. This is actually happening, isn’t it? Hesitantly, he presses the blade against the vertebrae that makes up Cross’ neck. “Like this?”

Gleeful at Sans accepting his weird knife fetish, he nods a little too hard and the sharp metal nicks his bone. He hisses, but when Sans tries to frantically pull away Cross grabs his wrist and pulls the blade back to his neck. “No! No, it’s okay, I like being scratched up a little bit.” 

Interesting. 

With that out of the way, he finally angles his cock against Cross’ cunt and slides home. His wet, tight heat is divine. Sans finds out that if he presses the knife a little bit harder when he thrusts, Cross’ pussy will squeeze around him like a vice. 

“Dude, holy shit.” Cross cries. “Harder, fuck me harder.”

Well, you don’t have to ask Sans twice. He pulls out until his cock almost slips away and slams back in with the force to rattle teeth. This causes another nick, and this time liquid comes gushing out of Cross like a river. He tries to say something, but Sans can’t make out what it is because his words are incomprehensible.

He bets it’s been a long time for Cross, too. 

He loses himself in the pleasure. Cross’ pussy is too perfect, the right amount of tight that borders painful for Sans. He likes the cramped feeling, it hugs parts of his dick that has him seeing stars. So, can you truly judge him for not lasting long? Besides, when he cums Cross follows seconds later. 

His cunt milks Sans for all he’s worth, pulling every last drop of Sans’ jizz into a willing pussy. The aftermath of it leaves his whole body shaking. He unironically feels boneless, and he collapses on top of Cross. Cross welcomes him with open arms, pulling him into an embrace. The knife drops somewhere to the side of them.

That’s dangerous. One of them could roll over in their sleep and lay right on top of it. But right now, Sans genuinely does not care. Dream land is calling his name, and he can deny the desire for sleep no longer. 

Cross pets the back of his skull as he drifts off, clearly desperate for as much physical affection he can get. Blood trickles steadily from his neck, but the wounds are superficial and can be dealt with tomorrow. For now, everything is perfect.

*

“I don’t trust this, Cross.”

“By this point, what do we have to lose?” Cross is just so, so tired. Sans has offered him help and he sees no reason as to why they should deny it. 

“I’ve got a bad feeling about this, that’s all.”

Cross scowls. Chara has a talent for putting him in a bad mood. “Why?” 

“I don’t know. Enjoy this while you can, I guess.” 

**Author's Note:**

> 44 people voted on that poll and 47% wanted Cross. That's a lot, I think? Poor ink and fresh! I had fun with this. I will definitely write more Cross in the future!!!!
> 
> Comments and Reviews are always appreciated


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